If it's just a small case of the old WB, it usually helps me to go for a walk. I get incredible plot insight while I'm walking and the only trouble with that is, I don't have pad nor paper with me and usually by the time I get home I forget. In bigger cases of WB, I've found writing things that don't have anything to do with my book helps. For example, a fan fiction serial called Coffeelandia which we do with my author group, www.naughtyninjas.net or even a blog post. This year I wrote a completely unrelated short story of 3000 words. It wasn't a romance - it was a fairly dire topic actually - but it helped get the words flow on my next romance again. It's like tricking your body and brain into writing.